DESCRIPTION: The long term goals are to identify the origins of neocortex, and the nature of the cellular and molecular events that lead to its formation from precursors common to both mammals and reptiles/birds. In order to address these issues, they must be approached as two separate, but related, questions. 1. Can we identify populations in adult nonmammals homologous with populations of adult neocortical neurons of mammals? Are specific cells and pathways common to ancestors of both mammals and reptiles/birds? 2. What are the cellular and molecular events underlying the transformation of the forebrain from nonmammals to mammals? How have the components of the telencephalon been modified to produce the mammalian cortex?